Will somebody kindly assist me in finding the purpose/nature of an old "socket" existing at the back upper portion (behind Driver's window) of the cabin of my truck (1967 FORD C600 squad body, with bodywork by Thibaultt and Morysville, formerly operationg in New Jersey).

See attached pictures (dimension is about diameter 3 inch). I can imagine one of the 3 following possibilities, as a kind of "socket" for holding: a)aerial radio antenna/mast; b)searchlight ; c)siren/PA loudspeaker.

Looks to me as if it used to be an adjustable antenna that was removed and caped. Looks very much like the type of mount found used for marine type VHF antennas that had a lever to bring it down for storage and bridges. I would check the other side of it and see what type of wire you find tucked away. .... Sorry did not see the post date on this for my reply.

Thank you for your contribution. It is indeed a distinctive possibility, although I am more inclined to believe that what was in there should probably be a PA loudspeaker as also advised by another Contributor.I checked on eBay and found one for sale (expensive though...) with a very similar socket.